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The suppressive effect of dexamethasone (Dex) on plasma cortisol and beta-lipotrophin (beta LPH) was investigated in patients with anorexia nervosa. Dex was given either orally, 1 mg at 2400 h, with blood sampling at 0800 h on the days before and after Dex, or by i.v. infusion starting at 1100 h (1 mg/h) for 4 h with sampling at 0800, 1100, 1500, 2000 and 2400 h and at 0800 h the following day. The plasma cortisol and beta LPH levels during oral or i.v. Dex administration were compared between patients and normally menstruating women of normal weight. The results showed that Dex administration depressed cortisol significantly (P less than 0.0001) during oral or i.v. infusion in most patients, without, however, suppressing it entirely as is the case in normal women. Moreover, during i.v. Dex infusion, the concentrations of cortisol escaped suppression and were higher than in normal women (less than 50 nmol/l) by 0800 h on the day following infusion. In the patients who were reinvestigated after re-feeding and weight gain (n = 9), a normal suppression of cortisol in response to i.v. Dex infusion was observed in only five cases and a slight failure to suppress, although concentrations were lower than before refeeding, was still evident in four. We concluded that, in anorexia nervosa, cortisol concentration rapidly escapes suppression by Dex administration, and that this escape is not related to the degree of starvation.